Pacemakers for generating artificial stimulating pulses for the heart, and which may be implanted in the body, are well known. Originally the electrical circuitry for such pacemakers was of analog design, but in recent years digital circuitry has been also employed. A digital approach to pacemakers has led to the evolution of programmable pacemakers--pacemakers having parameters such as pulse rates which are adjustable (programmable) once the pacemaker has been implanted. Programmable pacemakers are described in, for instance, British Pat. Nos. 1,385,954 and 1,398,875. Such pacemakers have circuitry to detect and decode signals transmitted outside the body and alter the program accordingly. In British Pat. No. 1,385,954 (claiming priority based on U.S. Ser. No. 141,694, in turn a parent of U.S. Pat. No. 3,805,796 to Tenz), the programming is accomplished by means of a magnetic field which is sensed by a magnetic reed switch; the opening and closing of the switch providing programming pulses to a program store. In British Pat. No. 1,398,875 (based on U.S. Pat. No 3,833,005 to Wingrove) the programming is by means of radio frequency transmission and reception.
It is desirable to miniaturize pacemaker components as far as possible, especially where implanted pacemakers are concerned, and although integrated circuit techniques can help enormously to achieve this aim, the battery size is still a major problem. The most recently-available miniature batteries having sufficient power and life for pacemaker usage are lithium batteries (both of the "solid" and "viscous" types), and such batteries are now employed in pacemakers. Unfortunately, lithium batteries only generate about 3 volts and although this voltage is sufficient to provide the supply voltage for, say, an integrated circuit pacemaker, it is insufficient, in itself, for the pacemaker output stage which needs to generate artificial stimulating pulses of at least 5 volts. Under certain circumstances, it is even desirable to generate pacing pulses of greater magnitude (e.g. about 7.5 volts). Although two or more lithium batteries can be employed for such purposes (and, indeed, have in the past been so employed), this militates against the desire for maximum miniaturization.